Drilling tools are used when drilling a well downhole. Drilling may also be performed in an existing well for making a branch well. While drilling a borehole into the subterranean formation, the fluid surrounding the drilling tool is filled with elements such as debris and formation pieces released from the formation. If the debris and formation pieces are not pumped up, they will interfere with and aggravate the drilling process.
The fluid containing debris and formation pieces is typically pumped up to above surface, after which the debris and formation pieces are filtrated from the fluid. Such processes are very energy consuming since the fluid has to be pumped all the way up to above surface only to be poured into the well again.
An attempt to filtrate debris and formation pieces from the fluid downhole while drilling is disclosed in DE 28 08 206, in which the drilling tool ejects the filtrated fluid out through the drilling head and has an intake of fluid in the part of the tool closest to the wireline. In this way, the fluid containing debris and formation pieces is forced along the side of the tool, resulting in that the debris and formation pieces are squeezed between the formation and the tool whereby the tool is at risk of getting stuck.
Furthermore, the debris and formation pieces forced along the side of the tool are pumped to above the tool. Thus, the debris and formation pieces fill the space above the tool and may obstruct the return path of the tool to above surface. This problem is particularly relevant in regard to wireline tools, which have a limited amount of power in relation to tools using coiled tubing drilling.